1. Field of the Invention
The present invention relates to a distributed document management system for managing document data in computers, such as host computers, workstations and PCs, connected by a network (hereinafter abbreviated to hosts). Such a system locates and stores the distributed data in the hosts, more particularly the present invention relates to a distributed document management system for managing a document update history and a domain update history in order to maintain a consistency between link information of a document and an actual storage location of the document.
2. Related Art of the Invention
A document management system may distribute and locate document data in hosts in a network. A variety of types of document data (for example, partial text data such as a chapter, paragraph, etc., and components of a document such as a graphic data, image data, photo, etc.) may be generated by a plurality of document writers in a plurality of hosts. Such data are connected by links describing storage locations and identification names of the respective document data, so that a document can be generated by combining the plurality of document data.
FIG. 1 is a schematic diagram showing data distributed and stored in hosts in a network, and their links. As shown in this figure, data "b" through "d" which will be the components of document data "a" stored in a host A, are respectively and independently stored in hosts A through C, and connected by links. A document whose components are respectively and independently stored, and connected by links as described above, is called a compound document.
The component data of a document includes text, a graphic, image, video, etc. Additionally, there are a variety of link forms for the component data. A compound document includes an integrated document connected by a hierarchical link, hypertext connected by a non-hierarchical link, etc. An HTML document is one type of compound document.
A link between data is represented by combining a domain, host, directory path, file name, database name, etc., which indicate a storage location and identification name of data. When a compound document is generated, a reference for the document can be described by writing the link information to a referencing document. Assuming that the document data "a" (text data) is a referencing document in FIG. 1, the link information of the data "b" through "d" are written to the document data "a".
If document data are distributed and located in hosts in a network, the information about the storage locations and identification names of the document data are required to reference or retrieve the document data, etc. For example, a storage location of the document data is represented by using a hierarchical domain name which indicates the location of a host and host name, and a directory path indicating the storage location of the document data in the host, in a system which uses a file system to store document data. Additionally, a file name is used as the identification name.
FIG. 2 exemplifies such a domain, host, and file system. Here, assume that the identification information in the format "host name. domain name. domain name 1. .cndot..cndot..cndot.. domain name n / directory name 1 / .cndot..cndot..cndot. / directory name n / file name" is used to describe the identification information. The identification information of text A shown in FIG. 2 can be represented as "Host A. Domain E. Domain A / Directory A / Directory B / Directory C / File A (Text A)".
If a compound document is generated by using the storage location and identification name of data as described above, the link information indicating the storage location and identification name of external document data is inserted into the compound document.
If document data is moved (in a host, or from host to host), if the name of the document data is changed, or if the name of the host or the name of the domain to which the host belongs is changed, the document data may sometimes not be retrieved, based on only the link information. This is because the storage location and identification name of document data are described as the link information in a compound document as described above.
If the storage location or identification name of document data indicated by link information is changed after such a compound document is generated, the link information relating to the document data to be changed, which is included in the compound document, must be updated. That is, all of the storage location and identification name indicated by the link information must be changed to the storage location and identification name after a change.
Accordingly, the following problems arise with the conventional method.
1) Since all items of related link information included in a compound document must be updated when document data is moved, or the name of the document data is changed, this process becomes complicated.
2) When the name of a host or the name of the domain to which the host belongs is changed, the link information which references the host and domain must be modified.
Since the above described process includes a search operation for document data in order to reference document data whose storage location or name is changed, it is difficult to implement. Therefore, if an access is unsuccessfully made, the retrieval of the document data is forced to be aborted.